Lubricating oil composition

ABSTRACT

A lubricant composition contains a lubricant base oil, (A) a detergent containing magnesium, (B) a compound containing boron, and (C) a zinc dialkyl dithiophosphate. The amount of component (A) is in the range of 200 to 1200 mass ppm [Mg] based on the mass of the lubricant composition, and the amount of component (C) is in the range of 300 to 1000 mass ppm [P] based on the mass of the lubricant composition. Component (C) includes a zinc dialkyl dithiophosphate having a primary alkyl group or a secondary alkyl group; the lubricant composition includes zinc dialkyl dithiophosphate having a secondary alkyl group; the mass ratio of the zinc dialkyl dithiophosphate having a primary alkyl group and the zinc dialkyl dithiophosphate having a secondary alkyl group is from 70:30 to 0:100; and the concentration of [B] is from 100 to 300 mass ppm based on the mass of the lubricant composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is the National Phase entry of International Patent Application No. PCT/IB2017/000897 filed on Aug. 2, 2017, which claims priority to Japanese Patent Application No. 20016-152180 filed Aug. 2, 2016, the entire contents of which are hereby incorporated by reference into this application.

FIELD

The present disclosure relates to a lubricating oil composition. Specifically, the present disclosure relates to a lubricating oil composition for an internal combustion engine, and particularly relates to a lubricating oil composition for a gasoline engine.

BACKGROUND

Lubricating oil compositions have been widely used in the automotive field, e.g., for internal combustion engines, automatic transmissions, gear oils, and the like. In recent years, a reduction in viscosity has been demanded for improving fuel efficiency. However, such a reduction in viscosity results in a decrease in the thickness of an oil film, thereby making it impossible to sufficiently reduce friction. Thus, molybdenum dithiocarbamate (MoDTC), which generates molybdenum disulfide under a boundary lubrication condition, thereby enabling friction to be reduced, has been conventionally used. In such a case, a calcium-based detergent is usually used in combination (for example, Japanese Unexamined Patent Publication (Kokai) No. 2013-199594 (Patent Literature 1)). However, the combination has a limitation on a reduction in friction and does not enable fuel efficiency to be sufficiently improved.

It has also been known to use magnesium-based detergents as detergents (for example, Japanese Unexamined Patent Publication (Kokai) No. 2011-184566 (Patent Literature 2) and Japanese Unexamined Patent Publication (Kokai) No. 2006-328265 (Patent Literature 3)). Use of such a magnesium-based detergent enables less friction to occur but causes wear to more easily occur than use of a calcium-based detergent.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication (Kokai) No. 2013-199594

Patent Literature 2: Japanese Unexamined Patent Publication (Kokai) No. 2011-184566

Patent Literature 3: Japanese Unexamined Patent Publication (Kokai) No. 2006-328265

SUMMARY Technical Problem

An object of the present disclosure is to provide a lubricating oil composition that enables friction to be reduced while ensuring wear prevention properties even when achieving low viscosity. In accordance with some embodiments, an object of the present disclosure is to provide a lubricating oil composition for an internal combustion engine and to provide a lubricating oil composition for a supercharged gasoline engine.

Solution to Problem

As a result of intensive examination, the present inventors found that the above objects are achieved by adding a particular amount of magnesium-based detergent and a particular amount of zinc dialkyldithiophosphate having a particular structure to a lubricant base oil and by defining the content of boron contained in a composition.

In other words, the present disclosure is directed to:

a lubricating oil composition comprising a lubricant base oil, (A) a detergent containing magnesium, (B) a boron-containing compound, and (C) a zinc dialkyldithiophosphate, wherein

an amount of component (A) is from 200 to 1200 ppm by weight in terms of a magnesium concentration [Mg] which is ppm by weight of magnesium based on the lubricating oil composition;

an amount of component (C) is from 300 to 1000 ppm by weight in terms of a phosphorus concentration [P] which is ppm by weight of phosphorus based on the lubricating oil composition;

component (C) is one or more selected from zinc dialkyldithiophosphates having a primary alkyl group and/or a secondary alkyl group, with the proviso that the lubricating oil composition comprises at least one zinc dialkyldithiophosphate having a secondary alkyl group, and a weight ratio of a zinc dialkyldithiophosphate having a primary alkyl group to a zinc dialkyldithiophosphate having a secondary alkyl group is from 0/100 to 70/30; and

a boron concentration [B] is from 100 to 300 ppm by weight based on the lubricating oil composition.

In some embodiments of the present disclosure, the lubricating oil composition further includes at least one feature of (1) to (7) described below.

(1) The lubricating oil composition comprises at least one ashless dispersant containing boron as the boron-containing compound (B).

(2) The lubricating oil composition further comprises a detergent (A′) containing calcium, and satisfies the following equation:

{[Mg]/([Mg]+[Ca])}×100≥5

where [Ca] represents a concentration of calcium in terms of ppm by weight based on the lubricating oil composition.

(3) The lubricating oil composition further comprises a friction modifier containing molybdenum, and satisfies the following equation:

[Mg]/[Mo]<2.5

where [Mo] represents a concentration of molybdenum in terms of ppm by weight based on the lubricating oil composition.

(4) The lubricating oil composition has a CCS viscosity of not more than 6.2 Pa·s at −35° C.

(5) The lubricating oil composition has a high-temperature high-shear viscosity (HTHS viscosity) of 1.5 to 2.9 mPa·s at 150° C.

(6) The lubricating oil composition has a kinematic viscosity of less than 9.3 mm²/s at 100° C.

(7) The lubricating oil composition is for use in an internal combustion engine.

The present disclosure further relates to a method for reducing friction while maintaining low wear by using the lubricating oil composition or the lubricating oil composition of any one of the embodiments (1) to (7) described above.

Effects of the Present Disclosure

The lubricating oil composition of the present disclosure enables friction to be reduced while ensuring wear prevention properties even when achieving low viscosity. The lubricating oil composition can be used as a lubricating oil composition for an internal combustion engine, and as a lubricating oil composition for a supercharged gasoline engine.

DETAILED DESCRIPTION Lubricant Base Oil

A lubricant base oil in the present disclosure is not particularly restricted. The lubricant base oil may be any of mineral oils and synthetic oils, which may be used singly or in combination.

Examples of the mineral oils include mineral oils obtained by distilling crude oil under atmospheric pressure to produce an ordinary pressure residual oil, distilling the ordinary pressure residual oil under reduced pressure to produce a lubricating oil distillate, and purifying the lubricating oil distillate by one or more treatments, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, and hydrogenation refining; and wax-isomerized mineral oils, GTL (Gas to Liquid) base oils, ATL (Asphalt to Liquid) base oils, vegetable oil-based base oils, and mixed-base oils thereof.

Examples of the synthetic oils include polybutenes or hydrogenated products thereof; poly-α-olefins such as 1-octene oligomer and 1-decene oligomer, or hydrogenated products thereof monoesters such as 2-ethylhexyl laurate, 2-ethylhexyl palmitate, and 2-ethylhexyl stearate; diesters such as ditridecyl glutarate, di-2-ethylhexyl adipate, di-isodecyl adipate, ditridecyl adipate, and di-2-ethylhexyl sebacate; polyol esters such as neopentyl glycol di-2-ethyl hexanoate, neopentyl glycol di-n-octanoate, neopentyl glycol di-n-decanoate, trimethylolpropane tri-n-octanoate, trimethylolpropane tri-n-decanoate, pentaerythritol tetra-n-pentanoate, pentaerythritol tetra-n-hexanoate, and pentaerythritol tetra-2-ethyl hexanoate; and aromatic synthetic oils such as alkylnaphthalenes, alkylbenzenes, and aromatic esters, or mixtures thereof.

The kinematic viscosity (mm²/s) of the lubricant base oil at 100° C. is, but not limited to, from 2 to 15 mm²/s, from 3 to 10 mm²/s, from 3 to 8 mm²/s, or from 3 to 6 mm²/s. When the kinematic viscosity is within the above range, the lubricating oil composition that allows an oil film to be sufficiently formed and has excellent lubricity and less vaporization loss can be obtained.

The viscosity index (VI) of the lubricant base oil is, but not limited to, not less than 100, not less than 120, or not less than 130. When the viscosity index is within the above range, viscosity at low temperature can be reduced while an oil film is retained at high temperature.

(A) Magnesium-Based Detergent

The lubricating oil composition of the present disclosure comprises a detergent containing magnesium (hereinafter referred to as “magnesium-based detergent”) as a component. The magnesium-based detergent is a compound containing magnesium. A magnesium-based detergent that has been used as a metal-based detergent in a lubricating oil composition can be used as the magnesium-based detergent. Examples thereof include, but are not limited to, magnesium sulfonates, magnesium phenates, and magnesium salicylates. In some embodiments, the magnesium-based detergent can include magnesium salicylate or magnesium sulfonate. Such magnesium-based detergents may be used singly, or in combination of two or more thereof.

The lubricating oil composition enables high-temperature cleaning performance and rust prevention properties demanded for a lubricating oil to be ensured by including the magnesium-based detergent as a component (A). In addition, friction can be reduced, and therefore, torque can be reduced, which effect fuel efficiency characteristics.

The magnesium-based detergent is added in such an amount that the magnesium concentration [Mg] ranges from 200 to 1200 ppm by weight, from 300 to 1100 ppm by weight, or from 400 to 1000 ppm by weight, based on the lubricating oil composition. When the amount of the magnesium-based detergent is more than the above upper limit, wear becomes excessively great. When the amount of the magnesium-based detergent is less than the above lower limit, the effect of reducing friction becomes low.

In some embodiments, the magnesium-based detergent is overbased. When the magnesium-based detergent is overbased, acid neutralization properties demanded for a lubricating oil can be ensured. When an overbased magnesium-based detergent is used, the overbased magnesium-based detergent may be mixed with a neutral magnesium- or calcium-based detergent.

The total base value of the magnesium-based detergent is, but not limited to, from 20 to 600 mgKOH/g, from 50 to 500 mgKOH/g, or from 100 to 450 mgKOH/g. When the total base value of the magnesium-based detergent is within the above range, acid neutralization properties, high-temperature cleaning performance, and rust prevention properties demanded for a lubricating oil can be ensured. When a mixture of two or more metal detergents is used, a total base value of the mixture is within the above range.

The content of magnesium in the magnesium-based detergent is from 0.5 to 20% by weight, from 1 to 16% by weight, or from 2 to 14% by weight. However, the magnesium-based detergent has only to be added in such an amount that magnesium is contained in the above amount in the lubricating oil composition.

When the lubricating oil composition of the present disclosure comprises a molybdenum-based friction modifier described later, the amount of the magnesium-based detergent satisfies the following equation (2):

[Mg]/[Mo]<2.5  (2)

where [Mo] represents the concentration of molybdenum in terms of ppm by weight based on the lubricating oil composition.

In some embodiments, the value of [Mg]/[Mo] is not more than 2.0, not more than 1.8, or not more than 1.5. When the value of [Mg]/[Mo] is not less than 2.5, wear may sometimes be too great. The value of [Mg]/[Mo] is not less than 0.1, more preferably not less than 0.2, or not less than 0.3.

The lubricating oil composition of the present disclosure may comprise another metal-based detergent in combination with the above magnesium-based detergent. The metal-based detergent may be a metal-based detergent which has been used in a lubricating oil composition. In some embodiments, a detergent (A′) containing calcium (hereinafter referred to as “calcium-based detergent”) may be used in combination. The lubricating oil composition enables high-temperature cleaning performance and rust prevention properties demanded for a lubricating oil to be further ensured by further comprising the calcium-based detergent.

The calcium-based detergent (A′) is a compound containing calcium. A calcium-based detergent that has been used as a metal-based detergent in a lubricating oil composition can be used as the calcium-based detergent (A′). Examples thereof include, but are not limited to, calcium sulfonates, calcium phenates, and calcium salicylates. Such calcium-based detergents may be used singly, or in combination of two or more thereof.

The amount of the component (A′) satisfies the following equation (1).

{[Mg]/([Mg]+[Ca])}×100≥5  (1)

where [Ca] represents the concentration of calcium in terms of ppm by weight based on the lubricating oil composition.

In some embodiments, the value of {[Mg]/([Mg]+[Ca])}×100 is not less than 10, or not less than 15. When the value is less than 5, the effect of reducing friction becomes low. In some embodiments, the value of {[Mg]/([Mg]+[Ca])}×100 is not more than 100, not more than 80, not more than 60, or not more than 50.

When the lubricating oil composition of the present disclosure further comprises a molybdenum-containing friction modifier described later, the following equation (3) is satisfied.

([Mg]+[Ca]/[Mo]≤3.0  (3)

where [Mo] represents the concentration of molybdenum in terms of ppm by weight based on the weight of the lubricating oil composition.

In some embodiments, the value of ([Mg]+[Ca])/[Mo] is not more than 2.8, not more than 2.6, or not more than 2.5. When the value of ([Mg]+[Ca])/[Mo] is more than 3.0, the effect of reducing torque may sometimes be low. In some embodiments, the value of ([Mg]+[Ca])/[Mo] is not less than 0.2, not less than 0.5, or not less than 1.0.

In some embodiments, the calcium-based detergent (A′) is overbased. When the calcium-based detergent is overbased, acid neutralization properties demanded for a lubricating oil can be ensured. When an overbased calcium-containing detergent is used, a neutral calcium-based detergent may be used in combination.

The total base value of the calcium-based detergent (A′) is, but not limited to, from 20 to 500 mgKOH/g, from 50 to 400 mgKOH/g, or from 100 to 350 mgKOH/g. When the total base value of the calcium-based detergent is within the above range, acid neutralization properties, high-temperature cleaning performance, and rust prevention properties demanded for a lubricating oil can be ensured. When a mixture of two or more metal detergents is used, a total base value of the mixture is within the above range.

The content of calcium in the calcium-based detergent (A′) is from 0.5 to 20% by weight, from 1 to 16% by weight, or from 2 to 14% by weight.

The lubricating oil composition of the present disclosure may comprise a sodium-based detergent as a metal-based detergent other than the above metal-based detergents as long as the effects of the present disclosure are not impaired. The sodium-based detergent is a compound containing sodium. Examples thereof include sodium sulfonates, sodium phenates, and sodium salicylates. Such sodium-based detergents may be used singly, or in combination of two or more thereof. The lubricating oil composition enables high-temperature cleaning performance and rust prevention properties demanded for a lubricating oil to be ensured by containing the sodium-based detergent. The sodium-based detergent can be used in combination with the magnesium-based detergent described above and any calcium-based detergent.

The total amount of the metal-based detergents in the lubricating oil composition of the present disclosure has only to be such an amount that the amount of magnesium contained in the above composition is within the specific range described above. The amounts of the added calcium- and sodium-based detergents can be restricted depending on the amount of the magnesium-based detergent.

(B) Boron-Containing Compound

The lubricating oil composition of the present disclosure comprises a boron-containing compound. The boron-containing compound may be a known compound containing boron that has been blended into a lubricating oil composition. In some embodiments, the boron-containing compound is a boron-containing ashless dispersant. Other examples of the boron-containing compound include alkali borate-based additives described later. In some embodiments, the lubricating oil composition of the present disclosure comprises at least one boron-containing ashless dispersant as the boron-containing compound.

The lubricating oil composition of the present disclosure is characterized in that the amount of boron contained in the composition is 100 to 300 ppm by weight based on the total weight of the composition. In some embodiments, the content of boron is from 120 to 280 ppm by weight, or from 150 to 250 ppm by weight. Accordingly, the above boron-containing compound, particularly the boron-containing ashless dispersant, is blended in such an amount that the amount of boron contained in the composition is within the above range. When the boron-containing ashless dispersant and another boron-containing compound are used in combination, the total amount of boron contained in the composition is adjusted to be within the above range. In some embodiments, the amount of the blended boron-containing ashless dispersant is from 0.1 to 5% by weight, from 0.3 to 4% by weight, or from 0.5 to 3% by weight, based on the total weight of the composition.

One boron-containing ashless dispersant may be used singly, or two or more thereof may be used in combination. Examples thereof include boron-containing ashless dispersants obtained by modifying (boronating) a succinimide compound with a boron compound such as boric acid or a borate. In the lubricating oil composition of the present disclosure, an ashless dispersant containing no boron may be also used in combination. When the boron-containing ashless dispersant and the ashless dispersant containing no boron are used in combination, the total amount of the ashless dispersants may be not more than 20% by weight, not more than 15% by weight, still more preferably not more than 10% by weight, or not more than 5% by weight, based on the total weight of the composition.

Examples of ashless dispersants include a nitrogen-containing compound having at least one straight- or branched-chain alkyl or alkenyl group having 40 to 500 carbon atoms, such as from 60 to 350 carbon atoms, per molecule, or derivatives thereof; Mannich dispersants; derivatives of mono-type or bis-type succinimides (for example, compounds having the structures of alkenyl succinimides); benzylamines having at least one alkyl or alkenyl group having 40 to 500 carbon atoms per molecule; polyamines having at least one alkyl or alkenyl group having 40 to 400 carbon atoms per molecule; or products obtained by modifying these compounds with boron compounds, carboxylic acids, phosphoric acid, and the like. One or more arbitrarily selected from such ashless dispersants may be blended. Boron-containing ashless dispersants are compounds obtained by modifying the above compounds with a boron compound. Particularly, boron-containing ashless dispersants may include derivatives of mono-type or bis-type succinimides, and still more particularly, compounds obtained by modifying (boronating) an alkenyl succinimide compound with a boron compound such as boric acid or borates.

Boronated succinimide derivatives are produced by known methods. The methods are not particularly limited. For example, such a mono-type or bis-type succinimide derivative is obtained by allowing a compound having an alkyl or alkenyl group having 40 to 500 carbon atoms to react with a maleic anhydride at 100 to 200° C. to produce an alkyl succinic acid or an alkenyl succinic acid and by allowing the alkyl succinic acid or the alkenyl succinic acid and a polyamine to react with each other. Examples of the polyamine include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine. A mono-type succinimide derivative can be represented by, for example, the following formula (a). A bis-type succinimide derivative can be represented by, for example, the following formula (b).

In the above formulae, each R¹ independently is an alkyl or alkenyl group having 40 to 400 carbon atoms, m is an integer of from 1 to 20, and n is an integer of from 0 to 20. In some embodiments, the boronated succinimide derivative may be a bis-type succinimide compound. Mono-type and bis-type succinimide derivatives may be used in combination, two or more mono-type succinimide derivatives may be used in combination, or two or more bis-type succinimide derivatives may be used in combination.

A boronated succinimide derivative is obtained by allowing the above succinimide derivative and a boron compound to react with each other. Examples of the boron compound include boric acid, boric anhydride, boric acid esters, boron oxide, and boron halides. Boronated succinimide derivatives may be used singly, or in combination of two or more thereof.

Derivatives of nitrogen-containing compounds are known as other ashless dispersants. Examples thereof include: so-called oxygen-containing organic compound-modified compounds obtained by allowing the above nitrogen-containing compound (i.e., the nitrogen-containing compound having at least one straight- or branched-chain alkyl or alkenyl group having 40 to 500 carbon atoms, or from 60 to 350 carbon atoms, per molecule) to react with a monocarboxylic acid having 1 to 30 carbon atoms, such as fatty acid, a polycarboxylic acid having 2 to 30 carbon atoms, such as oxalic acid, phthalic acid, trimellitic acid, or pyromellitic acid, or an anhydride or ester compound thereof, an alkylene oxide having 2 to 6 carbon atoms, or a hydroxy(poly)oxyalkylene carbonate, and then neutralizing or amidating some or all of remaining amino and/or imino groups; so-called boron-modified compounds obtained by allowing boric acid to act on the above nitrogen-containing compound and then neutralizing or amidating some or all of remaining amino and/or imino groups; so-called phosphoric acid-modified compounds obtained by allowing phosphoric acid to act on the above nitrogen-containing compound and then neutralizing or amidating some or all of remaining amino and/or imino groups; sulfur-modified compounds obtained by allowing sulfur compounds to act on the above nitrogen-containing compound; and modified compounds obtained by subjecting the above nitrogen-containing compound to a combination of two or more modifications selected from modification with oxygen-containing organic compounds, boron modification, phosphoric acid modification, and sulfur modification.

In some embodiments, the ashless dispersants may include boric acid-modified compounds of the alkenyl succinimide derivatives, particularly boric acid-modified compounds of the bis-type alkenyl succinimide derivatives, so that heat resistance is further improved by being used in combination with the above base oil.

The number-average molecular weight (Mn) of the ashless dispersant is, but not limited to, not less than 2000, not less than 2500, not less than 3000, or not less than 5000, and not more than 15000. When the number-average molecular weight of the ashless dispersant is less than the above lower limit, dispersibility may be insufficient. When the number-average molecular weight of the ashless dispersant is more than the above upper limit, viscosity may be excessively high, flowability may be insufficient, and it may cause deposits to be increased.

An alkali borate-based additive may be added as another boron-containing compound. The alkali borate-based additive contains an alkali metal borate hydrate, and can be represented by the following formula.

M₂O.xB₂O₃.yH₂O

where M is an alkali metal, x is 2.5 to 4.5, and y is 1.0 to 4.8.

Examples of the alkali borate-based additive include lithium borate hydrates, sodium borate hydrates, potassium borate hydrates, rubidium borate hydrates, and cesium borate hydrates. In some embodiments, potassium borate hydrates and sodium borate hydrates are the alkali borate-based additive. In some embodiments, and potassium borate hydrates are the alkali borate-based additive. The average particle diameter of alkali metal borate hydrate particles is not more than 1 micron (μm). In the alkali metal borate hydrate used in the present disclosure, the ratio of boron to an alkali metal is in a range of about 2.5:1 to 4.5:1. The alkali borate-based additive is added in such an amount that the amount of boron is 2 to 300 ppm by weight based on the total weight of the lubricating oil composition.

Additional examples of other boron-containing compounds include: potassium borates such as potassium metaborate, potassium tetraborate, potassium pentaborate, potassium hexaborate, and potassium octaborate; calcium borate sulfonate; and calcium borate salicylate.

(C) Zinc Dialkyldithiophosphate

The lubricating oil composition of the present disclosure comprises a zinc dialkyldithiophosphate (ZnDTP (also referred to as “ZDDP”)). This compound functions as an anti-wear agent, and is represented by the following formula (4).

In formula (4), R² and R³ may be the same as or different from each other and each represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 26 carbon atoms. Examples of the monovalent hydrocarbon group include: primary or secondary alkyl groups having 1 to 26 carbon atoms; alkenyl groups having 2 to 26 carbon atoms; cycloalkyl groups having 6 to 26 carbon atoms; aryl groups, alkylaryl groups, or arylalkyl groups having 6 to 26 carbon atoms; and hydrocarbon groups containing an ester bond, an ether bond, an alcohol group, or a carboxyl group. The primary alkyl groups mean that in the substituents R² and R³, carbon atoms directly bound to oxygen atoms in the zinc dialkyldithiophosphate are primary carbon atoms. Similarly, the secondary alkyl groups mean that in the substituents R² and R³, the carbon atoms directly bound to the oxygen atoms in the zinc dialkyldithiophosphate are secondary carbon atoms. In some embodiments, each of R² and R³ independently is a primary or secondary alkyl group having 3 to 12 carbon atoms, a cycloalkyl group having 8 to 18 carbon atoms, or an alkylaryl group having 8 to 18 carbon atoms. In the present disclosure, however, at least one of R² and R³ is a primary or secondary alkyl group. The primary alkyl group has 3 to 12 carbon atoms, or from 4 to 10 carbon atoms. Examples thereof include a propyl group, a butyl group, a pentyl group, a hexyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, a 2-ethylhexyl group, and a 2,5-dimethylhexyl group. Such a secondary alkyl group has 3 to 12 carbon atoms, or from 3 to 10 carbon atoms. Examples thereof include an isopropyl group, a secondary butyl group, an isopentyl group, and an isohexyl group.

The lubricating oil composition of the present disclosure comprises one or more selected from zinc dialkyldithiophosphates having a primary alkyl group and/or a secondary alkyl group. The lubricating oil composition comprises a zinc dialkyldithiophosphate having a secondary alkyl group. In other words, the present disclosure includes three embodiments: the first embodiment in which the lubricating oil composition comprises both of a zinc dialkyldithiophosphate having a primary alkyl group and a zinc dialkyldithiophosphate having a secondary alkyl group; the second embodiment in which the lubricating oil composition comprises a zinc dialkyldithiophosphate having both of a primary alkyl group and a secondary alkyl group; and the third embodiment in which the lubricating oil composition comprises a zinc dialkyldithiophosphate having a secondary alkyl group and no zinc dialkyldithiophosphate having a primary alkyl group. In some embodiments, the lubricating oil includes the first embodiment in which a zinc dialkyldithiophosphate having a primary alkyl group and a zinc dialkyldithiophosphate having a secondary alkyl group are used in combination. When the lubricating oil composition comprises no zinc dialkyldithiophosphate having a secondary alkyl group, favorable wear prevention properties are unable to be ensured. The present disclosure is characterized in that the lubricating oil composition comprises a zinc dialkyldithiophosphate having a primary alkyl group and a zinc dialkyldithiophosphate having a secondary alkyl group at a weight ratio of 0/100 to 70/30. The ratio is from 5/95 to 65/35, from 10/90 to 60/40, or from 20/80 to 50/50. When the content of the zinc dialkyldithiophosphate having a primary alkyl group is more than the above upper limit, wear resistance may unfavorably deteriorate.

The content of the zinc dialkyldithiophosphate in the lubricating oil composition is such a content that the concentration [P] of phosphorus contained in the zinc dialkyldithiophosphate is 300 to 1000 ppm by weight, from 400 to 1000 ppm by weight, from 500 to 1000 ppm by weight, or from 600 to 900 ppm by weight, based on the total weight of the lubricating oil composition.

In the present disclosure, a torque reduction rate is improved by adjusting the relationship (combination) of the amount of boron contained in the lubricating oil composition and the weight ratio of the zinc dialkyldithiophosphate having a primary alkyl group (hereinafter simply referred to as “primary zinc dialkyldithiophosphate”) to the zinc dialkyldithiophosphate having a secondary alkyl group (hereinafter simply referred to as “secondary zinc dialkyldithiophosphate”). The combination may be adjusted as appropriate so that the amount of boron is within a range of 100 to 300 ppm by weight, or from 120 to 280 ppm by weight, or from 150 to 250 ppm by weight, based on the total amount of the composition, and so that the weight ratio of a primary zinc dialkyldithiophosphate to a secondary zinc dialkyldithiophosphate is within a range of 1/100 to 70/30, or from 5/95 to 65/35, or from 10/90 to 60/40, or from 20/80 to 50/50. The total amount of zinc dialkyldithiophosphates is adjusted in order that the total concentration (ppm by weight) of phosphorus may be within the above range. The lubricating oil composition obtained in such a manner enables both of favorable friction prevention properties and wear prevention properties to be achieved even when viscosity is low.

The lubricating oil composition of the present disclosure may further comprise an anti-wear agent other than the zinc dialkyldithiophosphate. Examples thereof include compounds represented by the above formula, in which each of R² and R³ independently is a hydrogen atom or a monovalent hydrocarbon group having 1 to 26 carbon atoms, which is not an alkyl group. Examples of the monovalent hydrocarbon groups include alkenyl groups having 2 to 26 carbon atoms; cycloalkyl groups having 6 to 26 carbon atoms; aryl groups, alkylaryl groups, and arylalkyl groups having 6 to 26 carbon atoms; and hydrocarbon groups containing an ester bond, an ether bond, an alcohol group, or a carboxyl group. In some embodiments, R² and R³ are cycloalkyl groups having 8 to 18 carbon atoms and alkylaryl groups having 8 to 18 carbon atoms, and may be the same as or different from each other. Zinc dithiocarbamate (ZnDTC) may be used in combination therewith.

At least one compound selected from phosphate- and phosphite-based phosphorus compounds represented by the following formulae (5) and (6), and metal salts and amine salts thereof may be used in combination.

In above formula (5), R⁶ is a monovalent hydrocarbon group having 1 to 30 carbon atoms, each of R⁴ and R⁵ independently is a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms, and k is 0 or 1.

In above formula (6), R⁹ is a monovalent hydrocarbon group having 1 to 30 carbon atoms, each of R⁷ and R⁸ independently is a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms, and t is 0 or 1.

Examples of the monovalent hydrocarbon groups having 1 to 30 carbon atoms, represented by R⁴ to R⁹ in above formulae (5) and (6), include alkyl groups, cycloalkyl groups, alkenyl groups, alkyl-substituted cycloalkyl groups, aryl groups, alkyl-substituted aryl groups, and arylalkyl groups. In some embodiments, the monovalent hydrocarbon groups are alkyl groups having 1 to 30 carbon atoms or aryl groups having 6 to 24 carbon atoms. In some embodiments, the monovalent hydrocarbon groups are alkyl groups having 3 to 18 carbon atoms, or alkyl groups having 4 to 15 carbon atoms.

Examples of the phosphorus compound represented by above formula (5) include phosphite monoesters and (hydrocarbyl) phosphonites having one of the above hydrocarbon groups having 1 to 30 carbon atoms; phosphite diesters, monothiophosphite diesters, and (hydrocarbyl) phosphonite monoesters having two of the above hydrocarbon groups having 1 to 30 carbon atoms; phosphite triesters and (hydrocarbyl) phosphonite diesters having three of the above hydrocarbon groups having 1 to 30 carbon atoms; and mixtures thereof.

A metal salt or amine salt of the phosphorus compound represented by above formula (5) or (6) can be obtained by allowing a metal base such as a metal oxide, a metal hydroxide, a metal carbonate, or a metal chloride, a nitrogen compound such as ammonia or an amine compound having only a hydrocarbon group or a hydroxyl group-containing hydrocarbon group having 1 to 30 carbon atoms in a molecule thereof, or the like to act on the phosphorus compound represented by formula (5) or (6), followed by neutralizing part or all of the remaining acidic hydrogen. Examples of a metal in the above metal base include alkali metals such as lithium, sodium, potassium, and cesium; alkaline-earth metals such as calcium, magnesium, and barium; and heavy metals such as zinc, copper, iron, lead, nickel, silver, and manganese (excluding molybdenum). In some embodiments, the metal in the above metal base includes zinc or alkaline-earth metals such as calcium and magnesium. In some embodiments, the metal in the above metal base is zinc.

The zinc dialkyldithiophosphate may be added in such an amount that the content of phosphorus originated from the zinc dialkyldithiophosphate is within the above specific range, as described above. When the lubricating oil composition comprises another anti-wear agent, the anti-wear agent may be blended into the lubricating oil composition in the total amount of the anti-wear agents including the zinc dialkyldithiophosphate of 0.1 to 5% by weight, or from 0.2 to 3% by weight.

The lubricating oil composition of the present disclosure may comprise various additives as optional components in addition to the above components. The lubricating oil composition may comprise, for example, a molybdenum-based friction modifier or a viscosity index improver.

Molybdenum-Based Friction Modifier

The friction modifier containing molybdenum (hereinafter referred to as “molybdenum-based friction modifier”) is not particularly limited. A friction modifier containing molybdenum can be used as the molybdenum-based friction modifier. The molybdenum-based friction modifier is a compound containing molybdenum. Examples thereof include organic molybdenum compounds containing sulfur such as molybdenum dithiophosphate (MoDTP) and molybdenum dithiocarbamate (MoDTC); complexes of molybdenum compounds and sulfur-containing organic compounds or other organic compounds; and complexes of sulfur-containing molybdenum compounds such as molybdenum sulfide and molybdate sulfide, and alkenyl succinimides. Examples of the above molybdenum compounds include molybdenum oxides such as molybdenum dioxide and molybdenum trioxide; molybdic acids such as orthomolybdic acid, paramolybdic acid, and (poly)molybdic sulfide; molybdates such as metal salts and ammonium salts of the molybdic acids; molybdenum sulfides such as molybdenum disulfide, molybdenum trisulfide, molybdenum pentasulfide, and molybdenum polysulfide; molybdate sulfides; metal salts and amine salts of molybdate sulfides; and molybdenum halides such as molybdenum chloride. Examples of the above sulfur-containing organic compounds include alkyl(thio)xanthate, thiadiazole, mercaptothiadiazole, thiocarbonate, tetrahydrocarbylthiuram disulfide, bis(di(thio)hydrocarbyldithiophosphonate) disulfide, organic (poly)sulfides, and sulfate esters. In some embodiments, the friction modifier includes organic molybdenum compounds such as molybdenum dithiophosphate (MoDTP) and molybdenum dithiocarbamate (MoDTC).

Molybdenum dithiocarbamate (MoDTC) is a compound represented by following formula [I], and molybdenum dithiophosphate (MoDTP) is a compound represented by following formula [II].

In above formulae [I] and [II], R₁ to R₈ may be the same as or different from each other, and are monovalent hydrocarbon groups having 1 to 30 carbon atoms. The hydrocarbon group may be straight or branched. Examples of the monovalent hydrocarbon groups include straight- or branched-chain alkyl groups having 1 to 30 carbon atoms; alkenyl groups having 2 to 30 carbon atoms; cycloalkyl groups having 4 to 30 carbon atoms; and aryl groups, alkylaryl groups, or arylalkyl groups having 6 to 30 carbon atoms. The binding position of the alkyl group in an arylalkyl group is arbitrary. More specifically, examples of alkyl groups include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, and branched-chain alkyl groups thereof. In some embodiments, the monovalent hydrocarbon groups may be alkyl group groups having 3 to 8 carbon atoms. In addition, X₁ and X₂ are oxygen atoms or sulfur atoms, and Y₁ and Y₂ are oxygen atoms or sulfur atoms.

An organic molybdenum compound containing no sulfur can also be used as the friction modifier. Examples of such compounds include molybdenum-amine complexes, molybdenum-succinimide complexes, molybdenum salts of organic acids, and molybdenum salts of alcohols.

A trinuclear molybdenum compound described in U.S. Pat. No. 5,906,968 can also be used as the friction modifier in the present disclosure.

The friction modifier is added in such an amount that the concentration [Mo] of molybdenum is within a range of 500 to 1500 ppm by weight, or from 600 to 1200 ppm by weight, based on the lubricating oil composition. When the amount of the friction modifier is more than the above upper limit, cleaning performance may deteriorate. When the amount of the friction modifier is less than the above lower limit, friction cannot be sufficiently reduced, and cleaning performance may deteriorate.

The friction modifier is contained in an amount that satisfies following equation (2):

[Mg]/[Mg]<2.5  (2)

as described above for component (A). [Mo] is the concentration of molybdenum in terms of ppm by weight based on the lubricating oil composition.

In some embodiments, the value of [Mg]/[Mo] is not more than 2.0, not more than 1.8, or not more than 1.5. The value of [Mg]/[Mo] is not less than 0.1, not less than 0.2, or not less than 0.3.

Viscosity Index Improver

Examples of the viscosity index improver include viscosity index improvers containing polymethacrylate, dispersion-type polymethacrylate, olefin copolymers (polyisobutylene, ethylene-propylene copolymer), dispersion-type olefin copolymers, polyalkylstyrene, hydrogenated styrene-butadiene copolymer, styrene-maleic anhydride ester copolymer, and star isoprene A comb-shaped polymer containing, in the main chain thereof, at least a repeating unit based on a polyolefin macromer and a repeating unit based on alkyl (meth)acrylate having an alkyl group having 1 to 30 carbon atoms can also be used.

The viscosity index improver comprises the above polymer and a diluent oil. The content of the viscosity index improver is from 0.01 to 20% by weight, from 0.02 to 10% by weight, or from 0.05 to 5% by weight, as the amount of polymer, based on the total amount of the composition. When the content of the viscosity index improver is less than the above lower limit, deterioration of viscosity temperature characteristics and low-temperature viscosity characteristics may occur. In contrast, when the content of the viscosity index improver is more than the above upper limit, deterioration of viscosity temperature characteristics and low-temperature viscosity characteristics may occur, further resulting in a great increase in product cost.

The lubricating oil composition of the present disclosure may further comprise other additives depending on purpose in order to improve the performance thereof. As such other additives, additives used in lubricating oil compositions can be used. Examples of other additives include additives such as antioxidants, friction modifiers other than the above friction modifier, corrosion inhibitors, antirust agents, pour-point depressants, demulsifiers, metal deactivators, and antifoaming agents.

Examples of the above antioxidants include ashless antioxidants such as phenol-based and amine-based ashless antioxidants, and metal-based antioxidants such as copper-based and molybdenum-based antioxidants. Examples of the phenol-based ashless antioxidants include 4,4′-methylenebis(2,6-di-tert-butylphenol), 4,4′-bis(2,6-di-tert-butylphenol), and isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate. Examples of the amine-based ashless antioxidants include phenyl-α-naphthylamine, alkylphenyl-α-naphthylamine, and dialkyl diphenylamine. In some embodiments, 0.1 to 5% by weight of an antioxidant is blended into the lubricating oil composition.

Examples of the friction modifiers other than the above friction modifier include esters, amines, amides, and sulfurized esters. In some embodiments, 0.01 to 3% by weight of a friction modifier is blended into the lubricating oil composition.

Examples of the above corrosion inhibitors include benzotriazole-based, tolyltriazole-based, thiadiazole-based, and imidazole-based compounds. Examples of the above antirust agents include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenylsuccinate esters, and polyvalent alcohol esters. In some embodiments, 0.01 to 5% by weight of each of a corrosion inhibitor and an antirust agent is blended into the lubricating oil composition.

For example, polymethacrylate-based polymers compatible with the lubricant base oil used can be used as the above pour-point depressants. In some embodiments, 0.01 to 3% by weight of a pour-point depressant is blended into the lubricating oil composition.

Examples of the above demulsifiers include polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and polyoxyethylene alkyl naphthyl ethers. In some embodiments, 0.01 to 5% by weight of a demulsifier is blended into the lubricating oil composition.

Examples of the above metal deactivators include imidazoline, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazole, benzotriazole and derivatives thereof, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazolyl-2,5-bisdialkyldithiocarbamate, 2-(alkyldithio)benzimidazole, β-(o-carboxybenzylthio)propionitrile. In some embodiments, 0.01 to 3% by weight of a metal deactivator is blended into the lubricating oil composition.

Examples of the above antifoaming agents include silicone oils having a kinematic viscosity of 1000 to 100000 mm²/s at 25° C., alkenyl succinic acid derivatives, esters of aliphatic polyhydroxy alcohols and long-chain fatty acids, methyl salicylate, and o-hydroxybenzyl alcohol. In some embodiments, 0.001 to 1% by weight of an antifoaming agent is blended into the lubricating oil composition.

The CCS viscosity of the lubricating oil composition of the present disclosure at −35° C. is, but not limited to, not more than 6.2 Pa·s, not more than 5.0 Pa·s, not more than 4.0 Pa·s, or not more than 3.5 Pa·s.

When the lubricating oil composition of the present disclosure comprises molybdenum, the amount of molybdenum in the lubricating oil composition and CCS viscosity at −35° C. satisfy following equation (7):

[CCS viscosity]/[Mo]≤0.01  (7)

where [CCS viscosity] represents the value (Pa·s) of the CCS viscosity of the lubricating oil composition at −35° C., and [Mo] represents the concentration of molybdenum in terms of ppm by weight based on the lubricating oil composition.

In some embodiments, the value of [CCS viscosity]/[Mo] is not more than 0.008, or not more than 0.005. A case in which, when the above value is more than 0.01, torque reduction rate may decrease or cleaning performance may deteriorate. The value of [CCS viscosity]/[Mo] is, but not limited to, not less than 0.002, or not less than 0.003.

The high-temperature high-shear viscosity (HTHS viscosity) of the lubricating oil composition of the present disclosure at 150° C. is, but not limited to, 1.5 to 2.9 mPa·s, from 1.7 to 2.8 mPa·s, or from 2.0 to 2.6 mPa·s.

The kinematic viscosity of the lubricating oil composition of the present disclosure at 100° C. is, but not limited to, less than 9.3 mm²/s, or less than 8.2 mm²/s.

The lubricating oil composition of the present disclosure exhibits the effects of having sufficient friction characteristics and wear characteristics and enabling a high torque reduction rate to be obtained even when viscosity is low, and can be used for an internal combustion engine and further for a supercharged gasoline engine.

EXAMPLES

The present disclosure will be described in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples.

Materials used in the examples and the comparative examples are as follows.

Lubricant Base Oil

Base oil derived from GTL having a kinematic viscosity at 100° C. of 4.1 mm²/s and VI of 127

(A) Magnesium-Based Detergent

Magnesium sulfonate having a total base value of 400 mgKOH/g and a magnesium content of 9.4% by weight

(A′) Calcium-Based Detergent

Calcium salicylate having a total base value of 230 mgKOH/g and a calcium content of 5.5% by weight

(B) Ashless Dispersant Containing Boron

Boronated succinimide compound which is a mixture of compounds represented by above formula (b), in which R¹ is polybutenyl, and n is 4 to 12; and has a boron content of 0.7% by weight, and a nitrogen content of 2.0% by weight

(B′) Ashless Dispersant Containing No Boron

Succinimide compound which is a mixture of compounds represented by above formula (b), in which R¹ is polybutenyl, and n is 4 to 12; and has a boron content of 0% by weight, and a nitrogen content of 1.0% by weight

(C) Anti-Wear Agent 1

Pri-ZnDTP which is a compound represented by following formula (4), in which both R² and R³ are primary alkyl groups having eight carbon atoms

(C) Anti-Wear Agent 2

Sec-ZnDTP which is a compound represented by above formula (4), in which R² is a secondary alkyl group having four carbon atoms, and R³ is a secondary alkyl group having six carbon atoms

(D) Friction Modifier

Molybdenum-based friction modifier: MoDTC having a molybdenum content of 10% by weight

(E) Viscosity Index Improver

Polymethacrylate

Other Additives

Antioxidant: phenol-based antioxidant

Antifoaming agent: dimethyl silicone

Examples 1 to 8 and Comparative Examples 1 to 6

Respective components having amounts listed in Tables 1 and 3 were mixed to prepare lubricating oil compositions. Amounts (part(s) by weight) listed in the tables are amounts (part(s) by weight) based on 100 parts by weight of the lubricating oil composition. Regarding the amounts of (A) magnesium-based detergent, (A′) calcium-based detergent, and (D) molybdenum-based friction modifier described in the tables, [Mg], [Ca], and [Mo] are contents (ppm by weight) of magnesium, calcium, and molybdenum, respectively, based on the lubricating oil composition. [B] listed in the tables represents the amount (ppm by weight) of boron based on the lubricating oil composition. The sum of the blended amounts of (C) anti-wear agents is 1 part by weight based on 100 parts by weight of the lubricating oil composition. The weight ratio of anti-wear agent 1 (zinc dialkyldithiophosphate having a primary alkyl group) to anti-wear agent 2 (zinc dialkyldithiophosphate having a secondary alkyl group) (primary zinc dialkyldithiophosphate/second zinc dialkyldithiophosphate (weight ratio)) is listed in the tables. [P] listed in the tables represents the amount (ppm by weight) of phosphorus based on the lubricating oil composition. The amounts of magnesium-based detergent and calcium-based detergent were adjusted so that the total molar quantities of magnesium and calcium contained in the detergents were as equal as possible in all the examples and the comparative examples.

The following tests on the obtained compositions were conducted. The results are listed in Tables 2 and 4.

(1) High-Temperature High-Shear Viscosity at 150° C. (HTHS150)

Measurement was performed according to ASTM D4683.

(2) CCS Viscosity at −35° C. (CCS Viscosity)

Measurement was performed according to ASTM D5293.

(3) Kinematic Viscosity at 100° C. (KV100)

Measurement was performed at 100° C. according to ASTM D445.

(4) Torque Reduction Rate

The lubricating oil compositions obtained in the examples and the comparative examples were used as test compositions, and the torques of the compositions were measured by a motoring test using a gasoline engine. As the engine, a Toyota 2ZR-FE 1.8 L inline four-cylinder engine was used. A torque meter was placed between a motor and the engine, and a torque was measured at an oil temperature of 80° C. and an engine speed of 700 RPM. A commercially available GF-5 0W-20 oil was used as a reference oil, and a torque was measured in a similar manner. The torque (T) of each test composition was compared with the torque (T₀) of the reference oil, and the reduction rate of the torque (T) from the torque of the reference oil ({(T₀−T)/T₀}×100) (%) was calculated. The greater reduction rate exhibits more favorable fuel efficiency. A lubricating oil composition having a reduction rate of not less than 9.0% was estimated as acceptable.

(5) Shell Wear Track Diameter

Measurement was performed according to the Shell four-ball test (ASTMD4172) except for a rotation number of 1800 rpm, a load of 40 kgf, a test temperature of 90° C., and a test time of 30 minutes. A lubricating oil composition resulting in a wear track diameter of not more than 0.7 mm was estimated as acceptable.

(6) Hot Tube Test (Evaluation of High-Temperature Cleaning Performance)

A lubricating oil composition at 0.3 mL/hr and air at 10 mL/sec were allowed to continuously flow into a glass tube having an inner diameter of 2 mm for 16 hours while maintaining the temperature of the glass tube at 270° C. The lacquer that adhered to the glass tube was compared with a color chart, and the lubricating oil compositions were scored based on a value of 10 for transparency and a value of 0 for black color. A higher score indicates better high-temperature cleaning performance. A lubricating oil composition having a score of 4.5 or more was evaluated as acceptable.

TABLE 1 Composition Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Lubricant base oil Balance Balance Balance Balance Balance Balance Balance Balance [A] Mg-based detergent [Mg] 400 500 600 400 400 400 400 500 [A′] Ca-based detergent [Ca] 1400 1400 1100 1400 1400 1400 1400 1400 [B] Boron-containing part(s) by weight 3 3 3 1.5 4.5 4.5 1.5 1.5 ashless dispersant [B] 200 200 200 100 300 300 100 100 [B′] Ashless dispersant part(s) by weight 0 0 0 1.5 0 0 1.5 1.5 containing no boron [C] Anti-wear agent 1 part(s) by weight 0.5 0 0.5 0.5 0 0.5 0.3 0 containing primary alkyl group Anti-wear agent 2 part(s) by weight 0.5 1 0.5 0.5 1 0.5 0.7 1 containing secondary alkyl group Primary zinc dialkyldithiophosphate/ 50/50 0/100 50/50 50/50 0/100 50/50 30/70 0/100 second zinc dialkyldithiophosphate (weight ratio) Total [P] 800 800 800 800 800 800 800 800 [D] Friction modifier [Mo] 800 800 800 800 800 800 800 800 [E] Viscosity index improver part(s) by weight 8 8 8 8 8 8 8 8 Other additive part(s) by weight 2 2 2 2 2 2 2 2 {[Mg]/([Mg] + [Ca])} × 100 22 26 35 22 22 22 22 26 ([Mg] + [Ca])/[Mo] 2.3 2.4 2.1 2.3 2.3 2.3 2.3 2.4 [Mg]/[Mo] 0.50 0.63 0.75 0.50 0.50 0.50 0.5 0.63

TABLE 2 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Evaluation CCS viscosity 3.1 3.1 3.1 3.1 3.1 3.3 3.1 3.0 results HTHS 150 2.3 2.4 2.3 2.3 2.3 2.3 2.3 2.3 KV 100 6.4 6.4 6.4 6.4 6.4 6.5 6.4 6.4 [CCS viscosity]/[Mo] 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 Torque reduction rate (%) 9.8 11.6 9.2 11.8 9.2 9.2 10.9 9.7 (Acceptable: ≥9.0) HTT 7.5 6.0 7.0 5.5 7.0 7.5 5.0 4.5 (Acceptable: ≥4.5) Wear resistance 0.7 0.7 0.7 0.7 0.7 0.6 0.7 0.7 (Acceptable: ≤0.7 mm)

TABLE 3 Comparative Comparative Comparative Comparative Comparative Comparative Composition Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Lubricant base oil Balance Balance Balance Balance Balance Balance [A] Mg-based detergent [Mg] 500 400 400 400 500 1400 [A′] Ca-based detergent [Ca] 1400 1400 1400 1400 1400 0 [B] Boron-containing part(s) by weight 0 0 1.5 4.5 7.5 3 ashless dispersant [B] 0 0 100 300 500 200 [B′] Ashless dispersant part(s) by weight 3 3 1.5 0 0 0 containing no boron [C] Anti-wear agent 1 part(s) by weight 0 0.5 1 1 0.5 0.5 containing primary alkyl group Anti-wear agent 2 part(s) by weight 1 0.5 0 0 0.5 0.5 containing secondary alkyl group Primary zinc dialkyldithiophosphate/ 0/100 50/50 100/0 100/0 50/50 50/50 second zinc dialkyldithiophosphate (weight ratio) Total [P] 800 800 800 800 800 800 [D] Friction modifier [Mo] 800 800 800 800 800 800 [E] Viscosity index improver part(s) by weight 8 8 8 8 8 8 Other additives part(s) by weight 2 2 2 2 2 2 {[Mg]/([Mg] + [Ca])} × 100 26 22 22 22 26 100 ([Mg] + [Ca])/[Mo] 2.4 2.3 2.3 2.3 2.4 1.8 [Mg]/[Mo] 0.63 0.50 0.50 0.50 0.63 1.75

TABLE 4 Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Evaluation CCS viscosity 3.1 3.1 3.0 3.3 3.5 3.1 results HTHS 150 2.3 2.3 2.3 2.3 2.3 2.3 KV 100 6.4 6.4 6.4 6.5 6.4 6.4 [CCS viscosity]/[Mo] 0.004 0.004 0.004 0.004 0.004 0.004 Torque reduction rate (%) 9.1 8.9 9.9 8.3 8.0 4.8 (Acceptable: ≥9.0) HTT 3.5 4.0 6.0 8.0 7.5 3.5 (Acceptable: ≥4.5) Wear resistance 0.7 0.8 1.0 0.6 0.6 0.6 (Acceptable: ≤0.7 mm)

As described in Table 2, the lubricating oil composition of the present disclosure exhibits low wear and has a high torque reduction rate and high high-temperature cleaning performance although it has a low kinematic viscosity at 100° C.

INDUSTRIAL APPLICABILITY

The lubricating oil composition of the present disclosure exhibits the effects of enabling friction to be reduced while ensuring wear prevention properties even when achieving low viscosity and of achieving a high torque reduction rate. In some embodiments, the lubricating oil composition of the present disclosure is a lubricating oil composition for an internal combustion engine, and as a lubricating oil composition for a supercharged gasoline engine. 

1. A lubricating oil composition comprising a lubricant base oil, (A) a detergent containing magnesium, (B) a boron-containing compound, and (C) a zinc dialkyldithiophosphate, wherein an amount of component (A) is from 200 to 1200 ppm by weight in terms of a magnesium concentration [Mg] which is ppm by weight of magnesium based on the lubricating oil composition; an amount of component (C) is from 300 to 1000 ppm by weight in terms of a phosphorus concentration [P] which is ppm by weight of phosphorus based on the lubricating oil composition; component (C) is one or more selected from zinc dialkyldithiophosphates having a primary alkyl group and/or a secondary alkyl group, wherein the lubricating oil composition comprises at least one zinc dialkyldithiophosphate having a secondary alkyl group, and a weight ratio of a zinc dialkyldithiophosphate having a primary alkyl group to a zinc dialkyldithiophosphate having a secondary alkyl group is from 0/100 to 70/30; and a boron concentration [B] is from 100 to 300 ppm by weight based on the lubricating oil composition.
 2. The lubricating oil composition according to claim 1, wherein the lubricating oil composition comprises at least one ashless dispersant containing boron as the boron-containing compound (B).
 3. The lubricating oil composition according to claim 1, wherein the lubricating oil composition further comprises a detergent (A′) containing calcium, and satisfies the following equation (1): {[Mg]/([Mg]+[Ca])}×100≥5  (1) where [Ca] represents a concentration of calcium in terms of ppm by weight based on the lubricating oil composition.
 4. The lubricating oil composition according to claim 1, further comprising a friction modifier containing molybdenum, and satisfies the following equation (2): [Mg]/[Mo]<2.5  (2) where [Mo] represents a concentration in terms of ppm by weight of molybdenum based on the lubricating oil composition.
 5. The lubricating oil composition according to claim 1, wherein the lubricating oil composition has a CCS viscosity of not more than 6.2 Pa·s at −35° C.
 6. The lubricating oil composition according to claim 1, wherein the lubricating oil composition has a high-temperature high-shear viscosity (HTHS viscosity) of 1.5 to 2.9 mPa·s at 150° C.
 7. The lubricating oil composition according to claim 1, wherein the lubricating oil composition has a kinematic viscosity of less than 9.3 mm²/s at 100° C.
 8. The lubricating oil composition according to claim 1, wherein the lubricating oil composition is for use in an internal combustion engine.
 9. The lubricating oil composition according to claim 2, wherein the lubricating oil composition further comprises a detergent (A′) containing calcium, and satisfies equation (1): {[Mg]/([Mg]+[Ca])}×100≥5  (1) where [Ca] represents a concentration of calcium in terms of ppm by weight based on the lubricating oil composition.
 10. The lubricating oil composition according to claim 2, further comprising a friction modifier containing molybdenum, and satisfies equation (2): [Mg]/[Mo]<2.5  (2) where [Mo] represents a concentration in terms of ppm by weight of molybdenum based on the lubricating oil composition.
 11. The lubricating oil composition according to claim 2, wherein the lubricating oil composition has a CCS viscosity of not more than 6.2 Pa·s at −35° C.
 12. The lubricating oil composition according to claim 2, wherein the lubricating oil composition has a high-temperature high-shear viscosity (HTHS viscosity) of 1.5 to 2.9 mPa·s at 150° C.
 13. The lubricating oil composition according to claim 2, wherein the lubricating oil composition has a kinematic viscosity of less than 9.3 mm²/s at 100° C.
 14. The lubricating oil composition according to claim 2, wherein the lubricating oil composition is for use in an internal combustion engine.
 15. The lubricating oil composition according to claim 3, further comprising a friction modifier containing molybdenum, and satisfies equation (2): [Mg]/[Mo]<2.5  (2) where [Mo] represents a concentration in terms of ppm by weight of molybdenum based on the lubricating oil composition.
 16. The lubricating oil composition according to claim 3, wherein the lubricating oil composition has a CCS viscosity of not more than 6.2 Pa·s at −35° C.
 17. The lubricating oil composition according to claim 3, wherein the lubricating oil composition has a high-temperature high-shear viscosity (HTHS viscosity) of 1.5 to 2.9 mPa·s at 150° C.
 18. The lubricating oil composition according to claim 3, wherein the lubricating oil composition has a kinematic viscosity of less than 9.3 mm²/s at 100° C.
 19. The lubricating oil composition according to claim 3, wherein the lubricating oil composition is for use in an internal combustion engine.
 20. The lubricating oil composition according to claim 4, wherein the lubricating oil composition has a CCS viscosity of not more than 6.2 Pa·s at −35° C. 